Effects of dynamic fixation on shear behaviour of porcine xenograft valves

To evaluate an alternative valve fixation technique, we measured the ability of glutaraldehyde-fixed valve tissue to undergo internal shearing during bending. Porcine aortic valves were fixed statically using conventional means, and dynamically while opening and closing repeatedly in a pulse tank. Using a polarized light microscopy technique developed previously, we measured shear deformation angles in thin sections of bent leaflet tissue and calculated shear strains. Statically-fixed leaflet tissue sheared only 1.2% +/- 2.29% (Mean +/- SD) when bent to curvatures of 2.0 mm-1, while dynamically-fixed tissue sheared 5.1% +/- 2.63% (significant at P less than 0.05). It is likely that dynamic fixation increases the ability of prosthetic valve leaflets to shear during bending by reducing the number of interfibre cross-links that would otherwise impede such deformations. Because shear strains reduce internal fibre strains and protect the leaflets against fatigue, prosthetic valves constructed from dynamically fixed tissue should experience lower stresses and hence last longer.